Environmental evidence of the first experiments in the evolution of complex life on Earth has been discovered by an international team of scientists.
Until now, scientists widely accepted that animals first appeared on Earth 635 million years ago.
But a team, led by Cardiff University, has discovered evidence of a much earlier ecosystem in the Franceville Basin near Gabon on the Atlantic coast of central Africa over 1.5 billion years ago.
Their study, presented in Precambrian Research, describes an episode of unique underwater volcanic activity following the collision of two continents, which created a nutrient-rich ‘laboratory’ for the earliest experiments in complex biological evolution.
Dr Ernest Chi Fru, lead author of the paper and reader at Cardiff University’s School of Earth and Environmental Sciences, said: “The availability of phosphorus in the environment is thought to be a key component in the evolution of life on Earth, particularly in the transition from organisms to simple unicellular to complex organisms such as animals and plants.”
We now know that the increase in the concentration of marine phosphorus and seawater oxygen is linked to an episode of biological evolution about 635 million years ago. Our study adds another, much earlier episode, 2.1 billion years ago.
Scientists have widely debated the validity of fossils of large macroorganisms from this period, which are the earliest of their kind in the geologic record.
But the Cardiff-led team identified a link between environmental change and nutrient enrichment before their emergence, which could have triggered their evolution.
The team’s geochemical analysis of marine sedimentary rocks deposited 2.1 billion years ago sheds new light on this highly controversial body of extraordinarily large fossils in the Francevillian Basin.
Dr Chi Fru added: “We think that submarine volcanoes, which followed the collision and suturing of the Congo and São Francisco cratons into one main body, further restricted and even cut off this part of the water from the global ocean to create a material nutrient- rich shallow inland marine sea.
“This created a localized environment where cyanobacterial photosynthesis was abundant over a long period of time, leading to the oxygenation of the local seawater and the generation of a large food source.
“This would have provided enough energy to drive the increased body size and more complex behavior observed in primitive animal-like simple life forms such as those found in fossils from this period.”
However, the confined nature of this body of water, along with the hostile conditions that existed beyond the confines of this environment for billions of years later, likely prevented these enigmatic life forms from gaining a global foothold, the researchers say.
Their study suggests that these observations may point to a two-step evolution of complex life on Earth.
The first step followed the first major increase in atmospheric oxygen content 2.1 billion years ago, and the second step followed a second increase in atmospheric oxygen levels about 1.5 billion years later.
While the first attempt did not spread, the second went on to create the biodiversity of animals we see on Earth today.
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